Acid/base and proton transport will be studied in phospholipid bilayer membranes, which are used as models for biological membranes. Planar bilayers will be formed in an open chamber designed so that mass transport and electrical properties can be measured simultaneously. Solute fluxes will be measured primarily with radiolabeled compounds, and proton conductances will be measured by standard electrical methods. The weak acids to be studied include medium to long-chain fatty acids, arachidonic acid and prostaglandins, bile acids, retinoic acid and related compounds, bilirubin, and weakly acidic drugs such as salicylates and related compounds. The specific aims are divided into two interrelated groups. The first group will focus on the mechanisms by which weak acids cause either proton conductance or nonionic proton transport. The second group will focus on the mechanisms by which the weak acids traverse the membrane en route to their target sites. The proton transport mechanism{s) will be determined by characterizing the concentration dependence, the pH dependence, the ionic (H or A ) conductances, the voltage dependence and the effects of agents which change either the membrane dipole potential (e.g., phloretin) or dielectric constant (e.g., chlorodecane). The weak acid transport mechanisms will be determined by characterizing the pH dependence, the voltage dependence, the dependence upon membrane thickness and the effects of serum albumin. The data from both groups of experiments will be used to predict proton conductances and weak acid transport rates in biological membranes. Specific biological questions to be asked include: What is the mechanism(s) of fatty acid toxicity in ischemia? How do salicylates cause a breakdown of the acid barrier in the gastric mucosa? Bow do salicylates damage mitochondria in Reye's syndrome? How do retinoic acid and bilirubin uncouple respiration and oxidative phosphorylation? How do fatty acids and bile acids traverse the membrane, i.e., what are the translocation and dissociation rate constants and rate limiting steps? Does serum albumin "facilitate" the transport of fatty acids and other organic anions through membranes and/or associated unstirred layers? Answers to these and other questions will increase our understanding of the mechanisms and functions of proton and acid/base transport in biological membranes and tissues. Since the weak acids to be studied are important in both normal and pathophysiology, the results should be useful in both the basic and clinical sciences.